Methods for using (2-imidazolin-2-ylamino) quinoxaline derivatives

ABSTRACT

A method of treating a mammal comprises administering to a mammal an effective amount to provide a reduction inflammation in the mammal of a compound selected from the group consisting of those having the formula: ##STR1## pharmaceutically acceptable acid addition salts thereof and mixtures thereof, wherein R 1  and R 4  are independently selected from the group consisting of H and alkyl radicals having 1 to 4 carbon atoms; the R 2  s are independently selected from H or alkyl radicals having 1 to 4 carbon atoms or are, together, oxo; the R 3  s are independently selected from H or alkyl radicals having 1 to 4 carbon atoms or are, together, oxo; the 2-imidazolin-2-ylamino group may be in any of the 5-, 6, 7- or 8- positions of the quinoxaline nucleus; and R 5 , R 6  and R 7  each is located in one of the remaining 5-, 6-, 7- or 8- positions of the quinoxaline nucleus and is independently selected from the group consisting of Cl, Br, H and alkyl radicals having 1 to 3 carbon atoms.

This application is a division of application Ser. No. 820,329, filedJan. 13, 1992, now U.S. Pat. No. 5,231,096 which, in turn, is acontinuation-in-part of application Ser. No. 758,696, filed Sep. 12,1991, now U.S. Pat. No. 5,204,347 which, in turn, is a division ofapplication Ser. No. 420,817, filed Oct. 12, 1989, now U.S. Pat. No.5,077,292; and a continuation-in-art of application Ser. No. 560,776,filed Jul. 31, 1990, now U.S. Pat. No. 5,112,822 which, in turn, is acontinuation-in-part of application Ser. No. 420,817, filed Oct. 12,1989, now U.S. Pat. No. 5,077,292. The disclosures of each of theseprior applications is incorporated in its entirety herein by reference.

BACKGROUND OF THE INVENTION

The present invention relates to novel substituted derivatives ofquinoxaline. More particularly, the invention relates to suchderivatives which are useful as therapeutic agents, for example, toeffect reduction in intraocular pressure, to increase renal fluid flowand to effect an alteration in the rate of fluid transport in thegastrointestinal tract.

Various quinoxaline derivatives have been suggested as therapeuticagents. For example, Danielewicz, et al U.S. Pat. No. 3,890,319discloses compounds as regulators of the cardiovascular system whichhave the following formula: ##STR2## where the 2-imidazolin-2-ylaminogroup may be in any of the 5-, 6-, 7- or 8- position of the quinoxalinenucleus; X, Y and Z may be in any of the remaining 5-, 6-, 7- or 8-positions and may be selected from hydrogen, halogen, lower alkyl, loweralkoxy or trifluoromethyl; and R is an optional substituent in eitherthe 2- or 3- position of the quinoxaline nucleus and may be hydrogen,lower alkyl or lower alkoxy.

SUMMARY OF THE INVENTION

New methods for treating mammals, preferably human beings, to provide adesired therapeutic effect have been discovered. By administering aneffective amount of one or more of certain compounds to a mammal, adesired therapeutic effect is provided in the mammal. Such desiredtherapeutic effects include reduction in peripheral pain,anesthetization of the central nervous system, constriction of one ormore blood vessels, reduction in or prevention of at least one effect ofischemia, decongestion of one or more nasal passages, and reduction inat least one effect of an inflammatory disorder.

The compounds which are administered in the methods of the presentinvention are those having the formula: ##STR3## and pharmaceuticallyacceptable acid addition salts thereof and mixtures thereof, wherein R₁and R₄ are independently selected from the group consisting of H andalkyl radicals having 1 to 4 carbon atoms; the R₂ s are independentlyselected from H or alkyl radicals having 1 to 4 carbon atoms or are,together, oxo; the R₃ s are independently selected from H or alkylradicals having 1 to 4 carbon atoms or are, together, oxo; the2-imidazolin-2-ylamino group may be in any of the 5-, 6-, 7- or 8-positions of the quinoxaline nucleus; and R₅, R₆ and R₇ each is locatedin one of the remaining 5-, 6-, 7- or 8- positions of the quinoxalinenucleus and is independently selected from the group consisting of C,Br, H and alkyl radicals having 1 to 3 carbon atoms.

Particularly useful compounds are those in which R₁ and R₄ are H, the2-imidazolin-2-ylamino group is in the 6- position of the quinoxalinenucleus, R₅ is selected from the group consisting of Cl, Br and alkylradicals containing 1 to 3 carbon atoms, more preferably Br, and is inthe 5- position of the quinoxaline nucleus, and R₆ and R₇ are H. Each ofthe R₂ s and each of the R₃ s is preferably independently selected fromH and alkyl radicals having 1 to 4 carbon atoms, more preferably from Hand methyl radical.

In one embodiment, at least one of the R₂ s and at least one of the R₃ sare H. At least one of the R₂ s or at least one of the R₃ s may bemethyl radical. The R₂ s and the R₃ s that are not alkyl, e.g., methyl,radicals, are H, or together is oxo. At least one of the R₂ s may bedifferent from at least one of the R₃ s.

Pharmaceutically acceptable acid addition salts of the compounds of theinvention are those formed from acids which form non-toxic additionsalts containing pharmaceutically acceptable anions, such as thehydrochloride, hydrobromide, hydroiodide, sulphate or bisulfate,phosphate or acid phosphate, acetate, maleate, fumarate, oxalate,lactate, tartrate, citrate, gluconate, saccharate and p-toluenesulphonate salts.

DETAILED DESCRIPTION OF THE INVENTION

The present invention involves methods for treating mammals to provideone or more desired therapeutic effects in the mammal. The presentmethods comprise administering an effective amount to provide thedesired therapeutic effect or effects in a mammal of at least onecompound, as described herein, to the mammal. Among the desiredtherapeutic effects are reduction in peripheral pain, anesthetization ofthe central nervous system, constriction of one or more blood vessels,reduction in or prevention of at least one effect of ischemia,decongestion of one or more nasal passages and reduction in at least oneeffect of an inflammatory disorder, for example, such disorderscharacterized by progressive joint and/or tissue deterioration. Thus,for example, the presently useful compounds may be effective as one ormore of the following: a peripheral pain killing agent, a generalanesthetic, a vaso-constricting agent, an agent for the treatment ofischemia, a nasal decongestant, and an anti-inflammatory agent. Oneimportant feature of many of the present methods is that the desiredtherapeutic effect is achieved with reduced side effects, in particularwith reduced effects on the blood pressure of the mammal to which thepresently useful compound or compounds are administered.

Any suitable method of administering the presently useful compound orcompounds to the mammal to be treated may be used. The particular methodof administration chosen is preferably one which allows the presentlyuseful compound or compounds to have the desired therapeutic effect inan effective manner, e.g., low medication concentration and lowincidence of side effects. In many applications, the presently usefulcompound or compounds are administered to a mammal in a mannersubstantially similar to that used to administer alpha agonists, inparticular alpha 2 agonists, to obtain the same or similar therapeuticeffect or effects.

Administration of the presently useful compounds for use in the methodsof this invention can include, but are not limited to, oral, parenteral,topical, intra-articular and other modes of systemic administration. Thecompounds are administered in a therapeutically effective amount eitheralone or in combination with a suitable pharmaceutically acceptablecarrier or excipient.

Depending on the intended mode of administration, the presently usefulcompound or compounds may be incorporated in any pharmaceuticallyacceptable dosage form, such as, for example, tablets, suppositories,pills, capsules, powders, liquids, suspensions, emulsions, aerosols orthe like, preferably in unit dosage forms suitable for singleadministration of precise dosages, or sustained release dosage forms forcontinuous controlled administration. Preferably the dosage form willinclude a pharmaceutically acceptable excipient and the presently usefulcompound or compounds and, in addition, may contain other medicinalagents, pharmaceutical agents, carriers, adjutants, etc.

For solid dosage forms, non-toxic solid carriers include, but are notlimited to, pharmaceutical grades of mannitol, lactose, starch,magnesium stearate, sodium saccharin, the polyalkylene glycols, talcum,cellulose, glucose, sucrose and magnesium carbonate. An example of asolid dosage form for carrying out the invention is a suppositorycontaining propylene glycol as the carrier. Liquid pharmaceuticallyadministrable dosage forms can, for example, comprise a solution orsuspension of one or more of the presently useful compounds and optionalpharmaceutical adjutants in a carrier, such as, for example, water,saline, aqueous dextrose, glycerol, ethanol and the like, to therebyform a solution or suspension. If desired, the pharmaceuticalcomposition to be administered may also contain minor amounts ofnontoxic auxiliary substances such as wetting or emulsifying agents, pHbuffering agents and the like. Typical examples of such auxiliary agentsare sodium acetate, sorbitan monolaurate, triethanolamine, sodiumacetate, triethanolamine oleate, etc. Actual methods of preparing suchdosage forms are known, or will be apparent, to those skilled in thisart; for example, see Remington's Pharmaceutical Sciences, MackPublishing Company, Easton, Pa., 16th Edition, 1980. The composition ofthe formulation to be administered, in any event, contains a quantity ofone or more of the presently useful compounds in an amount effective toprovide the desired therapeutic effect.

Parenteral administration is generally characterized by injection,either subcutaneously, intramuscularly or intravenously. Injectables canbe prepared in conventional forms, either as liquid solutions orsuspensions, solid forms suitable for solution or suspension in liquidprior to injection, or as emulsions. Suitable excipients are, forexample, water, saline, dextrose, glycerol, ethanol and the like. Inaddition, if desired, the injectable pharmaceutical compositions to beadministered may also contain minor amounts of non-toxic auxiliarysubstances such as wetting or emulsifying agents, pH buffering agentsand the like.

The amount of the presently useful compound or compounds administeredis, of course, dependent on the therapeutic effect or effects desired,on the specific mammal being treated, on the severity and nature of themammal's condition, on the manner of administration, on the potency andpharmacodynamics of the particular compound or compounds employed, andon the judgement of the prescribing physician. The therapeuticallyeffective dosage of the presently useful compound or compounds ispreferably in the range of about 0.5 or about 1 to about 100 mg/kg/day.

The presently useful compounds are as described above. Allstereoisomers, tautomers and mixtures thereof which comply with theconstraints of one or more formulae of the presently useful compoundsare included within the scope of the present invention. For example,both tautomers ##STR4## are within the scope of the present invention.

The presently useful compounds may be prepared in a manner analogous tothe procedures described in Danielewicz, et al U.S. Pat. No. 3,890,319for the production of the quinoxaline derivatives therein. This patentis hereby incorporated in its entirety by reference herein. Once a2-imidazolin-2-ylamino quinoxaline intermediate corresponding to thecompound described in Danielewicz, et al U.S. Pat. No. 3,890,319 isobtained, this 2-imidazolin-2-ylamino quinoxaline intermediate ishydrogenated to saturate any unsaturation at the 1-, 2-, 3-, and 4-positions of the quinoxaline nucleus.

Briefly, the 2-imidazolin-2-ylamino quinoxaline intermediates may beprepared by (1) reaction of the appropriate amino-quinoxaline withthiophosgene to form the corresponding isothiocyanate; and (2) reactingthis isothiocyanate with excess ethylene diamine to form thecorresponding beta-aminoethyl-thioureidoquinoxaline, which is thencyclized to the corresponding intermediate. Alternately, suchintermediates can be prepared by (1) reacting the correspondingaminoquinoxaline with benzoyl isothiocyanate to form the correspondingN-benzoyl thioureido compound, followed by hydrolysis to the thioureidocompound, or reaction of the aminoquinoxaline with ammonium thiocyanateto form the thioureido compound directly; (2) methylation to form theS-methyl deviation of the thioureido compound; and (3) reaction withethylene diamine to form the intermediate.

The 2-imidazolin-2-ylamino quinoxaline intermediate is then reacted tosaturate any unsaturation at the 1-, 2-, 3-, and 4- positions of thequinoxaline nucleus. For compounds in which R₁, the R₂ 's, the R₃ 's andR₄ are all to be H, the intermediate may be hydrogenated. Thishydrogenation preferably occurs with the intermediate dissolved in aliquid, e.g., a lower alcohol such as methanol, ethanol or the like. Acatalyst effective to promote the hydrogenation is preferably present.Examples of such catalysts include the platinum group metals, inparticular platinum, platinum group metal compounds, such as platinumoxide, and mixtures thereof. Hydrogen, e.g., free molecular hydrogen, ispresent in an amount at least sufficient to provide the desiredsaturation, preferably in an amount in excess of that required toprovide the desired saturation, of the intermediate. The temperature andpressure at which the hydrogenation occurs are preferably selected tomaintain the intermediate and final product substantially in the liquidphase. Temperatures in the range of about 10° C. to about 100° C. andpressures in the range of about 0.5 atmospheres to about 5 atmospheresoften provide acceptable results. These conditions are maintained for atime sufficient to provide the desired hydrogenation reaction. Thisperiod of time is often in the range of about 1 minute to about 2 hours.The final 2-imidazolin-2-ylamino tetrahydroquinoxaline is separated fromthe hydrogenation reaction mixture and recovered, e.g., usingconventional techniques.

For compounds in which R₁, the R₂ 's, the R₃ 's and R₄ are all to be Hand for compounds in which R₁ and R₄ are to be H and at least one of theR₂ s and/or at least one of the R₃ s are to be alkyl, the intermediatemay be reacted with a suitable hydride reducing agent. This reactionpreferably occurs with the intermediate and the hydride reducing agentdissolved in a liquid. Any suitable hydride reducing agent may beemployed. Examples of useful hydride reducing agents include NaBH₄,NaCNBH₄, LiAlH₄ and the like. The amount of hydride reducing agent usedshould be sufficient to saturate all the unsaturation present at the 1-,2-, 3- and 4- positions of the intermediate. Excess hydride reducingagent may be employed provided that no deterioration of the finaltetrahydroquinoxaline product results. The liquid employed should besuch as to act as an effective solvent for the intermediate and thehydride reducing agent, and may also function to facilitate, e.g.,activate, the reaction between the intermediate and hydride reducingagent. Examples of useful liquids include acetic acid, trifluoroaceticacid, tetrahydrofuran, diethyl ether and the like. The liquid employedis preferably selected so as to avoid excess hydride reducing agentreactivity. For example, where LiAlH₄ is used as the hydride reducingagent, the liquid is preferably tetrahydrofuran, diethyl ether and thelike. One or more co-solvents, e.g., lower alcohols, may also be used.The temperature and pressures at which the reaction occurs arepreferably selected to maintain the intermediate and final product inthe liquid phase. Temperatures in the range of about 0° C. to about 50°C. and pressures in the range of about 0.5 atmospheres to about 2atmospheres often provide acceptable results. Reaction time is chosen toallow the desired reaction to occur, and is often in the range of aboutone minute to about one hour. The final 2-imidazolin-2-ylaminotetraquinoxaline is separated from the reactive mixture and recovered,e.g., using conventional techniques, such as evaporation, deactivationof the excess hydride reducing agent, extraction and chromatographicseparation.

For compounds in which R₁ and/or R₄ are to be alkyl, the intermediate(having no substituents corresponding to R₁ and R₄) may be reacted witha suitable hydride reducing agent in the presence of a selected aldehydeor aldehydes. The aldehyde or aldehydes used are selected based on thespecific R₁ and/or R₄ alkyl group or groups desired. For example, if R₁and/or R₄ is to be methyl, formaldehyde is used, if R₁ and/or R₄ is tobe ethyl, acetaldehyde is used, etc. The reaction conditions used aresimilar to those described in the immediately preceding paragraph exceptthat the reaction time is often in the range of about 1 hour to about 24hours. The amount of aldehyde used may vary depending on the finalcompound desired. A mixture of final compounds, i.e., a compound inwhich both R₁ and R₄ are alkyl mixed with compounds in which only one ofR₁ or R₄ is alkyl, may be produced by the reaction. One or moreindividual tetrahydroquinoxalines useful in the present invention can beseparated and recovered from this mixture, e.g., using conventionaltechniques.

The presently useful compounds may be prepared from available startingmaterials. For example, 4-nitro-1,2-phenylenediamine may be reacted withan appropriate halide substituted carbonyl halide, in particular, abromide substituted carbonyl bromide. This reaction, which provides forsubstitution of one of the amine groups on the phenylene ring by thecarbonyl halide, is preferably conducted in a solvent and preferably ata temperature in the range of about 10° C. to about 50° C., inparticular about room temperature. Reaction pressure is preferably suchthat the solvent is maintained substantially in the liquid phase. Thereaction preferably occurs over a period of time in the range of about 2hours to about 24 hours. Examples of useful solvents include methylenechloride (CH₂ Cl₂), chloroform (CHCl₃), tetrahydrofuran and the like. Atrialkyl amine, e.g., triethylamine, may be used as part of the solventand/or to promote or facilitate the substitution reaction.

The resulting mixture of halo amide isomers are recovered preferably byconventional techniques, e.g., extraction, washing, drying,concentration, chromatography and the like, from the substitutionreaction mixture. The isomers are then cyclized. This cyclization ispreferably effected at a temperature in the range of about 10° C. toabout 50° C., in particular at room temperature, by contacting theisomers, preferably dissolved in a solvent such as methylene chloride,with a cyclizing agent, such as AgBF₄, AgNO₃ and the like. Reactionpressure is preferably such that the solvent is maintained substantiallyin the liquid phase. The reaction preferably occurs over a period oftime in the range of about 1 hour to about 24 hours. Conventionaltechniques, e.g., such as noted above, can be used to recover thecyclized isomers. Chromography can be used to separate the isomers andprovide them in substantially pure form.

The cyclized compound produced as described above, identified as anitro-substituted quinoxalinone, is hydrogenated to convert the nitrogroup to an amino group. This hydrogenation preferably occurs with thenitro- substituted quinoxalinone dissolved in a liquid, e.g., a loweralcohol such as methanol, ethanol or the like. A catalyst effective topromote the hydrogenation is preferably present. Examples of suchcatalysts include the platinum group metals, in particular platinum orpalladium, platinum group metal compounds, such as platinum oxide orpalladium oxide, and mixtures thereof. Hydrogen, e.g., free molecularhydrogen, is present in an amount at least sufficient to provide thedesired hydrogenation, preferably in an amount in excess of thatrequired to provide the desired hydrogenation. The temperature andpressure at which the hydrogenation occurs are preferably selected tomaintain the nitro-substituted quinoxalinone and hydrogenated productsubstantially in the liquid phase. Temperatures in the range of about10° C. to about 100° C. and pressures in the range of about 0.5atmospheres to about 5 atmospheres often provide acceptable results.These conditions are maintained for a time sufficient to provide thedesired hydrogenation reaction. This period of time is often in therange of about 1 hour to about 16 hours. The hydrogenated product isseparated from the hydrogenation reaction mixture and recovered, e.g.,using conventional techniques.

At this point, the hydrogenated product may be subjected to one or morereactions to include one or more groups in the compound, as desired. Forexample, in one embodiment, it is preferred that the final quinoxalinederivative of the present invention includes at least one halide group,in particular a bromo group, on the aromatic ring structure. In order toprovide such a bromo group, the above-noted hydrogenated product isbrominated. Such bromination can occur by dissolving the hydrogenatedproduct in a suitable solvent, e.g., glacial acetic acid,trifluoroacetic acid and the like, and contacting this solution withbromine. The mixture is preferably maintained at a suitably lowtemperature, e.g., in the range of about 10° C. to about 50° C., so thatthe degree of bromination can be controlled. Cooling or removing heatfrom the reaction mixture may be desirable. Room temperature brominationprovides satisfactory results. Reaction pressure is preferably such thatthe solvent is maintained substantially in the liquid phase. Thereaction preferably occurs over a period of time in the range of about0.25 hours to about 6 hours. Conventional techniques, e.g., vacuumfiltration, can be used to recover the brominated product, which may bea hydrobromide salt.

The above-noted hydrogenated product or substituted hydrogenated productis reacted with 2-imidazoline-2-sulfonic acid to produce a2-imidazolin-2-ylamino quinoxaline derivative useful in the presentinvention. Such derivatives include an oxo group. This reaction canoccur by dissolving the reactants in an appropriate solvent, e.g., analcohol such as isobutanol, and heating this solution to reflux atatmospheric pressure. Preferred reaction temperatures are in the rangeof about 70° C. to about 150° C. Reaction pressure is preferably suchthat the solvent is refluxed or maintained substantially in the liquidphase. The reaction preferably occurs over a period of time in the rangeof about 1 hour to about 24 hours. Conventional techniques, e.g.,concentration and chromatography, can be used to recover the desiredquinoxaline derivative.

The present quinoxaline derivatives which do not include an oxo groupcan be obtained by reacting the above-described oxo-containingquinoxaline derivatives to remove the oxo group. This can beaccomplished by dissolving the oxo-containing material in an appropriatesolvent, e.g., tetrahydrofuran, acetic acid, trifluoroacetic acid,diethyl ether and the like, and subjecting this solution to a hydridereducing agent, such as LiAlH₄, NaBH₄, NaCNBH₃ and the like. Reactiontemperatures in the range of about 20° C. to about 100° C. can be used.Conventional techniques, e.g., cooling, concentration andchromatography, can be employed to provide the present quinoxalinederivative which do not include an oxo group.

Specific examples of compounds which are useful in the present inventioninclude those which have the following formulas: ##STR5## ,pharmaceutically acceptable acid addition salts thereof and mixturesthereof. Compounds having formula (I), pharmaceutically acceptable acidaddition salts thereof and mixtures thereof are particularly useful.

The present compound or compounds may be included in a medicationcomposition together with one or more other components to provide amedication composition which can be effectively administered. Such othercomponents, e.g., carriers, anti-oxidants, bulking agents and the like,may be chosen from those materials which are conventional and well knownin the art, e.g., as being included in medication compositions withalpha 2 agonists.

The following non-limiting examples illustrate certain aspects of thepresent invention.

EXAMPLE 1 Preparation of5-Bromo-6-(2-imidazolin-2-ylamino)-1,2,3,4-tetrahydroquinoxaline1,2,4-Triaminobenzene dihydrochloride

To a suspension of 4-nitrophenylenediamine (Aldrich, 10 g, 65.3 mmol) inabsolute ethanol (240 ml) was added 600 mg of 10% by weight palladium oncharcoal catalyst. The container including the suspension was evacuatedand filled with hydrogen three times and the suspension was hydrogenatedat 18 psi until hydrogen uptake ceased. The reaction was slightlyexothermic and one refill of hydrogen was required. The resulting lightyellow solution, which darkens rapidly on contact with air, was filteredand concentrated to about 150 ml. Concentrated hydrochloric acid (12 ml)was added and the solid formed was filtered off. After drying in vacuoovernight, 12 g (a yield of 93%) of purple solid was obtained, m.p.224°-225° C. Using various analytical procedures, this solid wasdetermined to be 1,2,4-triaminobenzene dihydrochloride.

6-Aminoquinoxaline

Glyoxal sodium bisulfite adduct (Aldrich, 14.3 g, 50 mmol) was added insmall portions to a solution of 1,2,4-triaminobenzene dihydrochloride(9.8 g, 50 mmol) in 200 ml of 10% by weight sodium carbonate in water.The reaction mixture was heated to 100° C. for two hours and then cooledto 0° C. The crystals formed were filtered off and dried in vacuo togive a crude yield of 7.06 g (a yield of 97%) of brown crystals.Recrystallization from benzene gave 6.32 g (a yield of 87%) yellowcrystals, m.p. 157°-148° C. Using various analytical procedures, theseyellow crystals were determined to be 6-aminoquinoxaline.

6-Amino-5-bromoquinoxaline hydrobromide

6-Aminoquinoxaline (2.08 g, 14.4 mmol) was dissolved in 11.5 ml glacialacetic acid. The solution was cooled in water while a solution ofbromine (0.74 ml, 2.3 g, 14.4 mmol) in 1.5 ml glacial acetic acid wasadded slowly over 15 min. After stirring for an additional 30 min, theorange red solid formed was filtered off and washed thoroughly with dryether. The solid was dried in vacuo overnight to yield 4.44 g crudeproduct (a yield of 100%). The compound, 6-amino-5-bromoquinoxalinehydrobromide, had no definite melting point. A phase change (from finepowder to red crystals) was noticed at about 220° C. Decomposition wasobserved at about 245° C. It was used directly for the next step.

6-Amino-5-Bromoquinoxaline

The crude 6-amino-5-bromoquinoxaline from above was dissolved in waterand saturated sodium bisulfite solution was added until the resultingsolution tested negative with starch-iodide paper. The solution was thenbasified with 2N sodium hydroxide and extracted thoroughly with ethylacetate. The organic extract was dried over magnesium sulfate andconcentrated under reduced pressure to give the free base. The crudeproduct was recrystallized from boiling benzene to give yellow crystals,m.p. 155°-156° C. Using various analytical procedures, the yellowcrystals were determined to be 6-amino-5-bromoquinoxaline. The yield was82%.

5-Bromo-6-isothiocyanatoquinoxaline

The crude hydrobromide product previously noted (4.27 g, 14.0 mmol) wasdissolved in 60 ml of water and thiophosgene (Aldrich, 1.28 ml, 16.8mmol) was added in small portions with vigorous stirring. After 2 hours,the red color of the solution was discharged. The solid formed wasfiltered off and washed thoroughly with water. After drying in vacuo at25° C., 3.38 g (a yield of 90%) of brick red crystals was obtained, m.p.157°-158° C. A portion of this material was further purified by columnchromatography to give white crystals, m.p. 157°-158° C. Using variousanalytical procedures, these crystals were determined to be5-bromo-6-isothiocyanatoquinoxaline.

5-Bromo-6(-N-(2-aminoethyl)thioureido)quinoxaline

A solution of the isothiocyanate (3.25 g, 12.2 mmol) in 145 ml benzenewas added to a solution of ethylenediamine (Aldrich, 5.43 g, 90.0 mmol)in 18 ml benzene at 25° C. over 2 hours. After stirring for a further 30min., the supernatant was poured off. The oil which remained was washedby swirling with dry ether three times and used directly for the nextstep.

A portion of this product was further purified by column chromatography(SiO₂, CHCl₃) for characterization. A white solid was recovered whichdecomposed at 175° C. with gas evolution (puffing). This white solid wasdetermined to be 5-bromo-6(-N-2-(aminoethyl)thioureido) quinoxaline.

5-Bromo-6-(2-imidazolin-2-ylamino)quinoxaline

The crude product from above was dissolved in 100 ml dry methanol andthe brown solution was refluxed for 19 hours until hydrogen sulfide gaswas no longer evolved. The mixture was cooled to room temperature andconcentrated to about 50 ml. The yellow solid was filtered off and driedin vacuo; weight 2.52 g (a yield of 70%), mp 242°-244° C.

As the crude product was insoluble in most common organic solvents,initial purification was achieved by an acid-base extraction procedure.23 g of the crude product was dissolved in 100 ml 0.5N hydrochloricacid. The turbid yellow solution was filtered to give a clear orangeyellow solution which was extracted twice with ethyl acetate (2×10 ml).The aqueous phase was cooled to 0° C. and basified with 6N sodiumhydroxide, keeping the temperature of the solution below 15° C. at alltimes. The yellow solid which precipitated was filtered off and washedthoroughly with water until the washings were neutral to pH paper. Thesolid was dried overnight in vacuo to give 1.97 g yellow solid, m.p.249°-250° C. The recovery was about 88%.

Further purification was achieved by recrystallization as describedbelow. The partially purified product from above was dissolved in N,N-dimethylformamide (about 17 ml/g) at 100° C. with vigorous stirring.The solution was filtered hot and set aside to cool overnight. Thebright yellow crystals were collected by filtration, m.p. 252°-3° C.Recovery was from 65-77%. Using various analytical procedures, thebright yellow solid was determined to be5-bromo-6-(2-imidazolin-2-ylamino) quinoxaline.

5-Bromo-6-(2-imidazolin-2-ylamino)-1,2,3,4-tetrahydroquinoxaline

A thick-waled Parr hydrogenation flask was charged with5-Bromo-6-(2-imidazolin-2-ylamino)quinoxaline (950 mg, 3.23 mmol),platinum oxide (95 mg) and 20 ml of methanol. The contents of the flaskwere contacted with hydrogen at 15 psi for 15 minutes. The resultingsolution was filtered through acid washed silicon dioxide, followed byevaporation of solvent. The resulting tan solid was chromatographed(SiO₂ ; 80/20 CHCl₃ /CH₃ OH saturated with NH₃ (g)) to yield 820 mg (ayield of 86%) of an off white solid, mp 218°-220° C. Using variousanalytical procedures, this off white solid was determined to be5-bromo-6-(2-imidazolin-2-ylamino)-1,2,3,4-tetrahydroquinoxaline.

EXAMPLE 2 Preparation of (±)2-Methyl-5-bromo-6-(2-imidazolin-2-ylamino)1,2,3,4-tetrahydroquinoxaline 2-Methyl-6-nitroquinoxaline

A solution of pyruvic aldehyde (Aldrich, 40% solution in H₂ O, 11.8 g,65.3 mmol) was added dropwise to a solution of4-nitro-1,2-phenylenediamine (Aldrich, 10 g, 65.3 mmol) in 150 ml of H₂O. The reaction mixture was heated to 80° C. for four hours. Thereaction was cooled to room temperature, diluted with H₂ O and extractedwith CHCl₃. The organic extracts were dried over MgSO₄ and evaporated toyield 10.7 g (a yield of 87%) of a brick red solid. Using variousanalytical procedures, this solid was determined to be 2-methyl-6nitroquinoxaline.

2-Methyl-6-Aminoquinoxaline

A thick-walled Parr hydrogenation flask was charged with2-methyl-6-nitroquinoxaline (10.0 g, 52.9) and CH₃ OH (200 ml). Theflask was flushed with a stream of N₂ and 10% by weight palladium oncharcoal (500 mg) was added. The flask was pressurized with H₂ to 50 psiand maintained at this pressure for three hours. The reaction mixturewas filtered through acid washed silicon dioxide and concentrated invacuo to yield a tan solid. The crude material was chromatographed (SiO₂;95/5 CHCl₃ /CH₃ OH saturated with NH₃ (g)) and recrystallized frombenzene to yield 7.4 g (a yield of 88%) of a tan solid. Using variousanalytical procedures, this tan solid was determined to be2-methyl-6-aminoquinoxaline.

2-Methyl-5-bromo-6-(2-imidazolin-2-ylamino) quinoxaline

By a series of reaction steps analogous to the reaction steps describedabove in Example 1, the title compound (mp. 260° C.) was preparedstarting with 2-methyl-6-aminoquinoxaline in place of6-aminoquinoxaline.

(+)2-methyl-5-Bromo-6-(2-imidazolin-2-ylamino-1, 2, 3,4-tetrahydroquinoxaline

A solution of 2-methyl-5-bromo-6-(2-imidazolin-2-ylamino) quinoxaline(40.5 mg, 0.132 mmol) in acetic acid was cooled to 10° C. and carefullytreated with NaBH₄ (5.0 mg, 0.132 mmol). The reaction mixture wasstirred for 15 minutes before the solvent was removed in vacuo. Theresidue was dissolved in H₂ O, treated with solid NaOH to pH 13 andextracted with CHCl₃. The combined organic extracts were dried overMgSO₄ and concentrated in vacuo to yield a yellow oil. The crudematerial was chromatographed (SiO₂, 80/20 CHCl₃ /CH₃ OH saturated withNH₃ (g)) to yield 21.8 mg (a yield of 53%) of a tan solid, mp 203°-205°C. Using various analytical procedures, this tan solid was determined tobe (±)2-methyl-5-bromo-(2-imidazolin-2-ylamino)-1,2,3,4-tetrahydroquinoxaline.

EXAMPLE 3 Preparation of (±)3-Methyl-5-bromo-6-(2-imidazolin-2ylamino)-1, 2, 3, 4-tetrahydroquinoxaline 3-Methyl-6-aminoquinoxaline

Pyruvic aldehyde (Aldrich, 892 mg, 4.95 mmol, 40% solution H₂ O) wasadded dropwise to a stirred solution of 1, 2, 4-triaminobenzenehydrochloride (1.0 g, 4.95 mmol) dissolved in 10% aqueous Na₂ CO₃ (15ml). The mixture was heated at 100° C. for two hours before cooling toroom temperature. The mixture was extracted with CHCl₃. The combinedorganic extracts were dried over MgSO₄ and concentrated in vacuo toyield a brown solid. The crude product was chromatographed (SiO₂, 95/5CHCl₃ /CH₃ OH saturated with NH₃ (g)) to yield 616 mg (a yield of 75%)of a yellow crystalline solid. An analytical sample was prepared byrecrystallization from benzene, mp 170°-173° C. Using various analyticalprocedures, the solid was determined to be 3-methyl-6-aminoquinoxaline.

(±)3-Methyl-5-bromo-6-(2-imidazolin-2-ylamino)-1, 2, 3,4-tetrahydroquinoxaline

By a series of reaction steps analogous to the reaction steps describedabove in Example 2, the title compound (mp 250°-251° C.) was preparedstarting with 3-methyl-6-aminoquinoxaline in place of2-methyl-6-aminoquinoxaline.

EXAMPLE 4 Preparation of5-Bromo-6-(2-imidazolin-2-ylamino)-1,4-dimethyl-1,2,3,4-tetrahydroquinoxaline,5-Bromo-6-(2-imidazolin-2-ylamino)-1-methyl-1,2,3,4-tetrahydroquinoxalineand5-Bromo-6-(2-imidazolin-2-ylamino)-4-methyl-1,2,3,4-tetrahydroquinxoaline

5-Bromo-6-(2-imidazolin-2-ylamino) quinoxaline (291 mg, 1 mmol) issuspended in CH₃ OH (2 ml) and treated with glacial acetic acid (1 ml).The reaction mixture is treated with NaCNBH₃ (252 mg, 4 mmol) andparaformaldehyde (450 mg, 5 mmol) and stirred at room temperature for4-8 hours. The reaction mixture is quenched with H₂ O (5 ml), basifiedwith solid NaOH (3 g) to pH>12 and extracted with CHCl₃. The CHCl₃extracts are dried over MgSO₄, concentrated invacuo and chromatographed(SiO₂,80/20 CHCl₃ /CH₃ OH saturated with NH₃ (g)) to yield theindividual title compounds. Each of these title compounds is tested andis found to have one or more useful therapeutic effects which knownalpha 2 agonists exhibit.

EXAMPLE 5 Preparation of5-Bromo-6-(2-imidazolin-2-ylamino)-1,4-diethyl-1,2,3,4-tetrahydroquinoxaline,5-Bromo-6-(2-imidazolin-2-ylamino)-1-ethyl-1,2,3,4-tetrahydroquinoxaline and5-Bromo-6-(2-imidazolin-2-ylamino)-4-ethyl-1,2,3,4-tetrahydroquinoxaline

The individual title compounds are prepared using the method illustratedin Example 5 except that acetaldehyde (220 mg, 5 mmol) is substitutedfor paraformaldehyde and the reaction time is 6-12 hours instead of 4-8hours. Each of these title compounds is tested and is found to have oneor more useful therapeutic effects which known alpha 2 agonists exhibit.

EXAMPLE 6 Preparation of1,2-dihydro-2,2-dimethyl-6-nitro-3-(4H)-quinoxalinone and3,4-dihydro-3,3-dimethyl-6-nitro-2-(1H)-quinoxalinone

To a stirred solution of 4-nitro-1,2-phenylenediamine (Aldrich, 5.0 g,32.6 mmol) and triethylamine (5.05 g, 50 mmol) in CH₂ Cl₂ (50 ml) isadded 2-bromo-2-methyl propionyl bromide (Aldrich 7.49 g, 32.6 mmol)dropwise. The mixture is stirred at room temperature until the startingmaterial (4-nitro-1,2-phenylenediamine) is consumed. The reaction isquenched with aqueous NH₄ Cl and the organic material is extracted withCH₂ Cl₂. The organic extract is washed with H₂ O (20 ml), dried overMgSO₄ and concentrated in vacuo. The residue is chromatographed onsilica gel with hexanes: ethyl acetate elution to yield a mixture ofbromo amide isomers. This mixture is dissolved in CH₂ Cl₂ (30 ml) andtreated with AgBF₄ (Aldrich, 6.36 g, 32.6 mmol) at room temperature toeffect cyclization. After the starting bromo amide isomers are consumed,the reaction is quenched with aqueous NH₄ Cl and the organic material isextracted with CH.sub. 2 Cl₂. The organic extract is washed with H₂ O(10 ml), dried over MgSO₄ and concentrated in vacuo. The residue ischromatographed on silica gel with hexanes: ethyl acetate elution toyield the title compounds in pure form. This chromatographing separatesthe title compounds and allows recovery of each of them individually.

EXAMPLE 7 Synthesis of6-amino-1,2-dihydro-2,2-dimethyl-6-(2-imidazolin-2-ylamino)-3-(4H)-quinoxalinone

A solution of 1,2-dihydro-2,2-dimethyl 6-nitro 3-(4H)-quinoxalinone(663mg, 3 mmol) in CH₃ OH (10 ml) is hydrogenated with 50 psi H₂ (g) at roomtemperature in the presence of a catalyst of 10% by weight palladium oncharcoal (50 mg). After the starting material is consumed, the solutionis filtered and concentrated in vacuo to yield6-amino-1,2-dihydro-2,2-dimethyl-3-(4H)-quinoxalinone.

EXAMPLE 8 Synthesis of6-amino-5-bromo-1,2-dihydro-2,2-dimethyl-3-(4H)-quinoxalinonehydrobromide

A solution of 6-amino-1,2-dihydro-2,2-dimethyl-3-(4H)-quinoxalinone (250mg, 1.31 mmol) in glacial acetic acid (4 ml) is cooled using a waterbath. Bromine (210 mg, 1.31 mmol) in acetic acid (0.25 ml) is addeddropwise over a 5 minute period. The mixture is stirred at roomtemperature for 4 hours and the resulting precipitate is collected byvacuum filtration. The title compound is obtained in pure form afterdrying in vacuo.

EXAMPLE 9 Synthesis of 2-imidazoline-2-sulfonic acid

2-Imidazolidinethione (66.3 g, 650 mmol), Na₂ MoO₄ (5 g, 227 mmol) andNaCl (15 g. 256 mmol) were added to 300 ml H₂ O. Although somedissolution occurred, a solid residue remained in the liquid of themixture. The mixture was cooled to -10° C. using an immersion cooler.500 ml of a 30% (w/v) aqueous H₂ O₂ solution was placed in a jacketedcontrolled drip rate addition funnel and cooled to 0° C. using an ice/H₂O bath. The aqueous H₂ O₂ solution was added to the mixture at a rate of60 drops/minute. The mixture was stirred for 16 hours at -10° C. Duringthis time, the mixture changed from a white suspension to a dark bluesolution to a light blue suspension. At the end of 16 hours, a solid wasfiltered from the suspension and dried in vacuo. No further purificationwas needed. 57.8 g (a yield of 52.3%) of the title compound as a whitesolid, which was characterized spectroscopically, was recovered. Thissolid was stable when stored in the dark at 0° C. for at least 6 months.

EXAMPLE 10 Synthesis of 5-bromo-1,2dihydro-2,2-dimethyl-6-(2-imidazolin-2-ylamino)-3-(4H)-quinoxaline

A mixture of 6-amino-5-bromo-1,2-dihydro-2,2-dimethyl-3-(4H) -quinoxalinone hydrobromide (479 mg, 1 mmol) and 2-imidazoline-2-sulfonicacid (224 mg, 1.5 mmol) in isobutanol (5 ml) is heated at reflux untilthe starting hydrobromide material is consumed. The solvent is removedin vacuo and the residue chromatographed on silica gel with CHCl₃ : CH₃OH saturated with NH₃ (g) elution to yield the title compound.

EXAMPLE 11 Preparationof5-bromo-2,2-dimethyl-6-(2-imidazolin-2-ylamino)-1,2,3,4-tetrahydroquinoxaline

A suspension of 5-bromo-1,2-dihydro-2,2-dimethyl-0.45 mmol) and LiALH₄(17 mg, 0.45 mmol) in tetrahydrofuran (3 ml) is heated and maintained ata temperature of 50°-80° C. until the starting material is consumed. Themixture is cooled to 0° C., 2-3 drops of H₂ O is added and the mixtureis filtered. The solution is concentrated in vacuo to yield a residuewhich s chromatographed on silica gel with CHCl₃ : CH₃ OH saturated withNH₃ (g) elution to produce the title compound.

EXAMPLE 12 Preparation of5-bromo-3,4-dihydro-3,3-dimethyl-6-(2-imidazolin-2-ylamino)-2-(1H)-quinoxalinone

By a series of reaction steps analogous to the steps described above inExamples 7 to 10, the title compound is prepared starting with3,4-dihydro-3,3-dimethyl-6-nitro-2-(1H)-quinoxalinone in place of 1,2dihydro-2,2-dimethyl-6-nitro-3-(4H)-quinoxalinone.

EXAMPLE 13 Preparation of5-bromo-3,4-dihydro-3,3-dimethyl-6-(2-imidazolin-2-ylamino)-1,2,3,4-tetrahydro-quinoxaline

Using the procedure illustrated in Example 11, the title compound isprepared starting with5-bromo-3,4-dihydro-3,3-dimethyl-6-(2-imidazolin-2-ylamino)-2-(1H)-quinozalinonein place of5-bromo-1,2-dihydro-2,2-dimethyl-6-(2-imidazolin-2-ylamino)-3-(4H)-quinoxalinone.

EXAMPLES 14 TO 17

The quinoxaline derivatives produced in Examples 10 to 13 are tested foractivity using the following in vitro methods.

Rabbit Vas Deferens: Alpha 2 Adrenergic Receptors

New Zealand white rabbits (2-3 kg) are killed by CO₂ inhalation and thevasa deferentia is removed. The prostatic ends of the vasa deferentia(2-3 cm lengths) are mounted between platinum ring electrodes in 9 mlorgan baths and bathed in Krebs bicarbonate solution of the followingcomposition (millimolar): NaCl 118.0; KCl 4.7; CaCl₂ 2.5; MgSO₄ 1.2; KH₂PO₄ 1.2; glucose 11.0; NaHCO₃ 25.0; which solution is maintained at 35°C. and bubbled with 95% O₂ and 5% CO₂. The initial tension of the vasdeferens is 0.5 g. The tissues are left to equilibrate for 30 minutesbefore stimulation is started. Vasa are then field stimulated (0.1 Hz, 2ms pulse width at 90 mA) using a square wave stimulator (WPI A310Accupulser with A385 stimulus). The contractions of the tissue arerecorded isometrically using Grass FT03 force-displacement transducersand displayed on a Grass Model 7D polygraph. A cumulativeconcentration-response relationship is obtained for the quinoxalinederivative being tested with a 4 minute contact time at eachconcentration. Each of the quinoxaline derivatives of Examples 10 to 13is effective to reduce the response height. Therefore, such compoundsmay be properly classified as Alpha 2 agonists since they are alsoinhibited pharmacologically by treatment with rauwolscine.

EXAMPLES 18 to 21

Each of the quinoxaline derivatives produced in Examples 10 to 13 istested for renal and blood pressure effects using the following method.

Young male (20-24 weeks old) Sprague-Dawley rats are used. Underketamine (60 mg/kg b.wt. i.m.) and pentobarbital (i.p. to effect)anesthesia, medical grade plastic tubes are implanted into the abdominalaorta and vena cava via the femoral vessels. In addition, aSilastic-covered stainless steel cannula is sewn in the urinary bladder.After the surgery, the rats are housed individually and are allowed freeaccess to food and water until the day of the experiment.

For about 7 to 10 days before surgery and during recovery, the rats areaccustomed to a restraining cage by placement in the cage for 2 to 3hours every 2nd and 3rd day. The cage is designed for renal clearancestudies (a model G Restrainer sold by Braintree Scientific, Inc.,Braintree, Mass.). The animals' adjustment to the cage is judged by thestability of blood pressure and heart rate.

For an experiment, a rat is placed in the restraining cage, and thearterial line is connected to a Statham pressure transducer and aBeckman Dynograph R61 to monitor the mean arterial blood pressure,hereinafter referred to as MAP. The venous line is connected to aninfusion pump system for infusion of replacement fluid. The quinoxalinederivative is administered intraduodenally by cannula. The bladdercannula was extended with a silastic tube to facilitate collection ofurine in preweighed tubes. The volume of urine is measuredgravimetrically. Body weight is recorded before and after theexperiment.

Throughout the experiments, 0.9% NaCl containing 10% polyfructosan(Inutest) and 1% sodium PAH is infused at a rate of 20 microliters/min.An equilibration period of 60 minutes is followed by two consecutive 30minute control clearance periods. Then, the quinoxaline derivative isadministered for 90 minutes. Urine collection is resumed 10 minutesafter the start of quinoxaline derivative administration. By this timethe washout of the bladder cannula dead space (approximately 200microliters) is completed. Three additional clearance measurements aremade. Blood samples (150 microliters) are collected at the midpoint ofurine collections. Plasma is separated and saved for analyses, and thecells are resuspended in saline and returned to the animals. Water andsodium loss is carefully replaced i.v. by a variable speed infusionpump.

Results of these tests indicate that the present quinoxaline derivativesproduce renal effects, e.g., increased renal fluid flow. The effect onblood pressure of such derivatives is limited relative to such renaleffects.

EXAMPLES 22 TO 25

Each of the quinoxaline derivative produced in Examples 10 to 13 istested for anti-diarrheal effects and blood pressure effects using thefollowing method.

Cecectomies are performed in unfasted rats in a conventional manner. Thececectomized rats are put into individual wire-bottomed cages placedover sheets of clean paper, and deprived of food and water for theduration of the assay. The MAP is monitored, as described in Examples 17to 20, throughout the assay. Rats are given a 2 hour acclimatizationperiod prior to the start of the assay in order to eliminate sporadicepisodes of anxiety-induced defecation. During this period they areobserved also for consistent occurrences of pelleted feces; an animalproducing other than a pelleted stool is disqualified from the study.

Diarrhea is induced with oral administration of 16,16-dimethylprostaglandin E₂ (dmPGE₂ ) in 3.5% EtOH. The quinoxaline derivative isadministered by gavage after the onset of diarrheal episodes. The cagepapers are removed and examined at 30 minute intervals for dmPGE₂-induced diarrhea. Fecal output is recorded at each interval and fecalconsistency is assigned a numerical score in each experimental group asfollows: 1=normal pelleted stool; 2=soft-formed stools; 3=water stooland/or diarrhea. The fecal output index (FOI) is defined as thesummation of the number of defecation episodes and their rankedconsistency score within an observation period.

Results of these tests indicate that the quinoxaline derivativesproduced in Examples 10 to 13 provide substantial anti-diarrhealeffects. Further, such anti-diarrheal effects are produced with no orrelatively limited effects on blood pressure.

While this invention has been described with respect to various specificexamples and embodiments, it is to be understood that the invention isnot limited thereto and that it can be variously practiced within thescope of the following claims.

What is claimed is:
 1. A method of treating a mammal for a reduction ininflammation comprising administering to a mammal an effective amount ofa compound selected from the group consisting of those having theformula ##STR6## , pharmaceutically acceptable acid addition saltsthereof and mixtures thereof, wherein R₁ and R₄ are independentlyselected from the group consisting of H and alkyl radicals having 1 to 4carbon atoms; the R₂ s are independently selected from H or alkylradicals having 1 to 4 carbon atoms or are, together, oxo; the R₃ s areindependently selected from H or alkyl radicals having 1 to 4 carbonatoms or are, together, oxo; the 2-imidazolin-2-ylamino group may be inany of the 5-, 6-, 7- or 8- positions of the quinoxaline nucleus; andR₅, R₆ and R₈ each is located in one of the remaining 5-, 6-, 7- or 8-positions of the quinoxaline nucleus and is independently selected fromthe group consisting of Cl, Br, H and alkyl radicals having 1 to 3carbon atoms.
 2. The method of claim 1 wherein at least one of the R₂ sand at least one of the R₃ s is H.
 3. The method of claim 1 wherein the2-imidazolin-2-ylamino group is in the 6- position of the quinoxalinenucleus, R₅ is in the 5- position of the quinoxaline nucleus and isselected from the group consisting of Cl, Br and alkyl radicalscontaining 1 to 3 atoms, and R₆ and R₇ are both H.
 4. The method ofclaim 1 wherein each of R₁ and R₄ is H.
 5. The method of claim 1 whereineach of the R₂ s and each of the R₃ s is independently selected from thegroup consisting of H and alkyl radicals having 1 to 4 carbon atoms. 6.The method of claim 1 wherein at least one of the R₂ s is different fromat least one of the R₃ s.
 7. The method of claim 2 wherein one of the R₂s and one of the R₃ s are independently selected from the groupconsisting of H and methyl radical.
 8. The method of claim 1 wherein R₅is Br.
 9. The method of claim 1 wherein said formula is: ##STR7## 10.The method of claim 1 wherein said formula is: ##STR8##
 11. The methodof claim 1 wherein said formula is: ##STR9##
 12. The method of claim 1wherein said formula is: ##STR10##
 13. The method of claim 1 whereinsaid formula is: ##STR11##
 14. The method of claim 1 wherein saidformula is: ##STR12##
 15. The method of claim 1 wherein said formula is:##STR13##
 16. The method of claim 1 wherein said therapeutic effect is areduction in inflammation caused by an inflammatory disordercharacterized by progressive joint deterioration or progressive tissuedeterioration.